1. Field of the Invention
The present invention relates to an apparatus for long-term ventilation and drainage of the middle ear cavity via enhancement of the normal physiologic functions of the eustachian tube.
2. Background of the Art
Adequate ventilation and drainage is essential for normal middle ear function. The Eustachian tube is purported to function in middle ear ventilation, drainage, and protection Chronic Eustachian tube dysfunction has been implicated in the pathogenesis of many otologic problems and is thought to be a principal cause of surgical failures. Patients with chronic middle ear disease have often been shown to have a mechanical narrowing or stenosis of the Eustachian tube, usually at the isthmus (junction of the bony and cartilaginous portions). This stenosis prevents normal function of the Eustachian tube.
Various methods have been devised to restore middle ear ventilation and drainage in the setting of chronic Eustachian tube obstruction. These have included elaborate procedures to restore Eustachian tube patency such as Eustachian tube irradiation and complex surgical shunt procedures. These are highly morbid procedures that have failed to gain widespread acceptance.
Most surgical procedures performed at this time involve bypassing the blocked Eustachian tube by implantation of a surgical prosthesis, usually in the tympanic membrane (ear drum), for ventilation of the middle ear cavity via the external ear canal. An example of such a ventilation tube is that disclosed in U.S. Pat. No. 3,807,409 to Paparella et al. These devices are deficient for several reasons. The body naturally extrudes these prostheses over variable time intervals. While functioning, they create the dual problems of a tympanic membrane perforation and an embedded foreign body exposed to a non-sterile environment. In addition, placement of a ventilation tube at the time of tympanic membrane or middle ear reconstruction can disrupt graft healing. U.S. Pat. No. 4,695,275 to Bruce et al., describes another type of ventilation tube designed to resist extrusion from the tympanic membrane. This prosthesis can function for a longer period of time but has a high incidence of persistent ear drum perforation following extrusion or removal, in addition to the aforementioned deficiencies.
Several attempts have been made to create a prosthesis for permanent aeration of the middle ear cavity. These prostheses also ventilate the middle ear through the external ear canal, however, they require a more complicated surgical procedure for insertion. U.S. Pat. No. 3,982,545 to Silverstein, describes a silicone rubber tube inserted into the middle ear through a hole drilled in the bony external ear canal. This prosthesis requires frequent cleaning as it has a tendency to obstruct, especially when inserted simultaneously with chronic ear surgery. U.S. Pat. No. 5,047,053 to Jahn, describes a similar permanent ventilation tube composed of hydroxylapatite. This tube is capable of biointegration with the bony ear canal. However, it does not eliminate the problems of extrusion or obstruction. Once obstructed, a second surgical procedure is required to remove or replace it.
All of the aforementioned inventions seek to provide an alternative method for middle ear ventilation and drainage rather than attempting to resolve the obstruction of the Eustachian tube itself. Anatomical studies have demonstrated that middle ear secretions are propelled toward the Eustachian tube orifice and away from the tympanic membrane, thus limiting the utility of the above prostheses implanted in the tympanic membrane. These studies suggest that enhancement, rather than bypass of the natural drainage pathway, the Eustachian tube, would provide optimal ventilation and drainage.
U.S. Pat. No. 4,015,607 to Wright, III, discloses a prosthesis for implantation in the Eustachian tube designed to provide permanent middle ear ventilation. The design comprises a simple hollow silastic tube with an attached flange. Both preliminary results published by Wright, III et al. in Laryngoscope, pp. 207-214, vol. 87, 1977, and long-term results published in ORL, pp. 834-837, vol. 86, 1978, were promising in a highly selective group of patients. However, attempts to extend use of the prosthesis to cases of refractory otitis media were xe2x80x9calmost universally disappointingxe2x80x9d in that the lumen of the prosthesis was usually completely occluded. A simllar study by Lesinki et al. in Laryngoscope, pp. 1413-1427, vol. 90, 1980, failed to reproduce any positive results, revealing high rates of tube protrusion, extrusion, mucosal inflammation, and obstruction. Seventy-seven percent of these ears had to be re-explored with removal of the prosthesis.
U.S. Pat. No. 5,645,584 describes a tympanostomy tube used in the treatment of a middle ear disorder, which is made of pure titanium or a titanium alloy. The tympanostomy tube comprises an elongated tubular member having a lumen formed longitudinally therein, the tubular member having substantially uniform diameter over the length thereof. The tubular member defines a wall of substantially uniform thickness, and the wall has a concavity inwardly formed on a portion of the elongated tubular member in a circumferential direction at right angles to a longitudinal direction thereof. The concavity is spaced from one end of the tubular member to form a flange portion on the tubular member, the lumen being longitudinally different in diameter and having a smaller diameter at a position at which the concavity is formed than at a position at which the concavity is not formed.
Almost all permanent prostheses inserted in the body will eventually cause an inflammatory tissue response and either become obstructed by encrustation or rejected and extruded. Since all stent materials cause some degree of mucosal incorporation, removal of a permanent stent has the attendant risk of causing bleeding and tissue injury. A permanent prosthesis also carries risk of pressure-induced erosion and injury to the adjacent carotid artery. In addition, a permanent Eustachian tube prosthesis is not desirable in many circumstances, such as in pediatric patients, in whom Eustachian tube dysfunction tends to be transient.
It is an aspect of the present invention to provide a Eustachian tube stent of superior design that is specifically adapted to the Eustachian tube environment. Another aspect of this invention is to provide a stent that will remain in place for a sufficiently long period of time to effect condition mediation without promoting inflamatory tissue ingrowth and obstruction or causing discomfort to the patient. Yet another aspect of this invention is to provide a stent composed of a biodegradable material that will be absorbed in a predictable manner, thus obviating the need for a second surgical procedure to remove it. Still another aspect of this invention is to provide a stent that is capable of carrying and eluting a drug that will enhance Eustachian tube lubrication and opening of the tube, and will resist infection and blockage.
The present invention provides an apparatus for long-term ventilation of the middle ear cavity that solves all of the problems discussed above. The stent of the present invention is positioned in the Eustachian tube with its proximal end open to the middle ear cavity. The preferably eccentrically-placed flanges secure the proximal end of the stent at the tympanic orifice of the Eustachian tube and prevent migration of the stent. The stent is easily positioned in the Eustachian tube under direct visualization after the medical practitioner has incised or lifted the tympanic membrane. The stent is advanced under direct visualzation, preferably over a stylet, guide wire, or over a flexible endoscope. Once the stent is inserted, the tympanic membrane is allowed to heal without perforation or communication between the external ear and middle ear spaces. The stent may be inserted at any convenient opportunity, such as at the time of middle ear exploration or reconstructive surgery.
The stent is specially adapted to the Eustachian tube environment. It comprises a hollow tubular body, preferably consisting of a network of biodegradable polymeric fibers having a primarily longitudinal orientation. It maintains patency and enhances aeration and drainage without having to exert a radial expansile force on the Eustachian tube. The stent components preferably degrade at a programmed rate, the rate being designed to permit a pre-determined safe duration of mucosal contact. The stent is wide proximally but narrows past the stenosed isthmus of the Eustachian tube. The preferably, eccentrically-placed flanges project laterally so as not to interfere with normal middle ear mucociliary clearance at the superior and inferior aspects of the Eustachian tube. The flanges support the stent from slipping within the Eustachian tube. There is no specific ridge or structure on which they hook or are supported, as the tympanic orifice is a flat surface. However, the stellate (radial projection shape) shape supports the stent from slippage. The flanges also may be flexible and exert a radial force when compressed to lessen the radial projection. The stent falls short of the distal end of the Eustachian tube so as to prevent autophony and ascending infection. The distal end of the stent is collapsible or flexibly compressible so as to protect the middle ear from unsavory conditions in the nasal pharyrnx, including infection, excessive noise, or excessive positive pressures such as that produced by violent sneezing or coughing. While the entire stent may be somewhat flexible, it is one important embodiment that the distal end is more compressible than the proximal end. With that feature, with the Eustachian tube in the resting closed state, the distal end will be more collapsed/compressed than the proximal end. In this manner, the distal end will be significantly closed or collapsed while the proximal portion will maintain a constant opening pressure across the area of narrowing in the stent. The distal portion should be collapsed to prevent the sensitive middle ear and inner ear from being exposed to refluxed secretions and excessive noise or pressure.